The present invention relates to a semiconductor device and a method therein, and relates to, for example, a semiconductor device used as a wireless receiver of a Low-Intermediate Frequency (IF) system and a method therein.
Japanese Unexamined Patent Application Publication No. 2000-068752 discloses a superheterodyne wireless receiver including an antenna, a tuning circuit, a high-frequency wave amplification circuit, a local oscillator, a mixer, an IF filter, and an IF amplification circuit. Since the superheterodyne wireless receiver is a general receiver and has a high frequency stability and selectivity, it is used in a wide range of communications and broadcasting fields in mobile telephones, televisions, and radios.
A problem in the superheterodyne system is that an image signal is generated. The image signal is an interfering wave signal received by an antenna and is a signal that is folded back into a reception bandwidth of a desired wave signal after it passes through the mixer. When, for example, the frequency of the desired wave signal received by the antenna is represented by f_RF, the frequency of a local signal is represented by f_LO, and the frequency of the image signal is represented by f_IM, f_RF−f_LO=f_LO−f_IM is established when f_RF>f_LO.
In the superheterodyne system, it is known that the image signal is decayed by a filter such as a tuning circuit before the image signal is input to the mixer, thereby reducing degradation of the reception performance by the image signal.
Further, a wireless receiver of a Low-IF system, the configuration of which is the same as that of the superheterodyne receiver but the IF frequency of which is smaller than that of the superheterodyne receiver, is known. One of the advantages in the wireless receiver of the Low-IF system is that since the IF frequency of the Low-IF system is smaller than that of the superheterodyne system, digital processing at the subsequent stage can be easily performed.